RFC-2841: add codegen flag export symbols from executable

[csmoe]

Closes #84161
r? @nikomatsakis @Mark-Simulacrum

[crlf0710]

@csmoe Ping from triage, CI is still red here. Would you mind fixing that?

[nikomatsakis]

Hmm, do we have any tests for symbol visibility? Maybe in the run-make folder? It'd be good to have a test for this.

[crlf0710]

@csmoe Ping from triage, would you mind adding the tests?

[csmoe]

@bjorn3 -Cexport-executable-symbols seems not work at all as dlopen errors with undefined symbol: exported_symbol, RUSTC_LOG=rustc_codegen_ssa::back::linker=debug printed that the symbol was exported indeed:

 INFO rustc_codegen_ssa::back::link preparing Executable to "main"
DEBUG rustc_codegen_ssa::back::linker EXPORTED SYMBOLS:
DEBUG rustc_codegen_ssa::back::linker     exported_symbol;
DEBUG rustc_codegen_ssa::back::linker     main;
DEBUG rustc_codegen_ssa::back::linker     rust_eh_personality;

Need more help to move on 😿
(btw, don't know why the CI did not error on the test)

[bjorn3]

Are you on Linux or macOS? What is the full linker invocation?

[csmoe]

"cc" "-Wl,--version-script=/repo/rust/./rustcqC1COd/list" "-m64" "main.main.cbc7ddee-cgu.0.rcgu.o" "main.main.cbc7ddee-cgu.1.rcgu.o" "main.main.cbc7ddee-cgu.10.rcgu.o" "main.main.cbc7ddee-cgu.11.rcgu.o" "main.main.cbc7ddee-cgu.12.rcgu.o" "main.main.cbc7ddee-cgu.13.rcgu.o" "main.main.cbc7ddee-cgu.14.rcgu.o" "main.main.cbc7ddee-cgu.15.rcgu.o" "main.main.cbc7ddee-cgu.2.rcgu.o" "main.main.cbc7ddee-cgu.3.rcgu.o" "main.main.cbc7ddee-cgu.4.rcgu.o" "main.main.cbc7ddee-cgu.5.rcgu.o" "main.main.cbc7ddee-cgu.6.rcgu.o" "main.main.cbc7ddee-cgu.7.rcgu.o" "main.main.cbc7ddee-cgu.8.rcgu.o" "main.main.cbc7ddee-cgu.9.rcgu.o" "main.4kqwyhdgeomtzpxx.rcgu.o" "-Wl,--as-needed" "-L" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,--start-group" "-Wl,-Bstatic" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-ea06e5b9ebe84ef4.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-608126472e4595bf.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libminiz_oxide-96b872de832ae456.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libadler-c96f7126ed0a8243.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libobject-d4333fc5a8e6acd5.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libmemchr-286e391a7bef4a33.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libaddr2line-9b3b5b41ef9d89ac.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libgimli-a01624f3c4d2f24b.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd_detect-606d386967062702.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_demangle-9fec6174a0598006.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libhashbrown-612142634ae08506.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_alloc-8a18ecd4776dc12c.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-11234a29b766d417.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcfg_if-5c49a6fde622d4a9.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-01242e2bb437fc18.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-a1d9b6c563f72c92.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_core-5a76a6f677cfd881.rlib" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-99c01d738b9e1246.rlib" "-Wl,--end-group" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-8ee0ab4b35b97256.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-Wl,--eh-frame-hdr" "-Wl,-znoexecstack" "-L" "/repo/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "main" "-Wl,--gc-sections" "-pie" "-Wl,-zrelro" "-Wl,-znow" "-nodefaultlibs"

@bjorn3 linux, cc args as above.

[bjorn3]

Could you compile with -Csave-temps and post contents of the version script passed to -Wl,--version-script=?

[bjorn3]

Maybe --gc-keep-exported is necessary?

When --gc-sections is enabled, this option prevents garbage collection of unused input sections that contain global symbols having default or protected visibility. This
option is intended to be used for executables where unreferenced sections would otherwise be garbage collected regardless of the external visibility of contained symbols.
Note that this option has no effect when linking shared objects since it is already the default behaviour. This option is only supported for ELF format targets.

[csmoe]

@bjorn3 version-script:

08:40 $ cat rustcXKEpHW/list
{
  global:
    exported_symbol;
    main;
    rust_eh_personality;

  local:
    *;
};

--gc-keep-exported is not available in old gcc(v6.3.0), I'll try a newer.

[bors]

💔 Test failed - checks-actions

[bjorn3]

The test needs to be ignored on nvptx64-nvidia-cuda. Maybe an // only-unix annotation works? Not sure if that is valid though.

[csmoe]

only-unix seems not working, as it ignored linux. I just limited the test with only-linux.

[bjorn3]

👍 Could you please squash? I noticed that one of the commits introduced merge conflict markers which another solves again. And besides, this is pretty much an atimic change. r=me after squashing

[csmoe]

@bors r=@bjorn3

[bors]

@csmoe: 🔑 Insufficient privileges: Not in reviewers

[bjorn3]

@bors r+

[bors]

📌 Commit 6674c94 has been approved by bjorn3

It is now in the queue for this repository.

[bors]

⌛ Testing commit 6674c94 with merge dc2d232...

[bors]

☀️ Test successful - checks-actions
Approved by: bjorn3
Pushing dc2d232 to master...

[bjorn3]

That only took 10 tries...

[rust-timer]

Finished benchmarking commit (dc2d232): comparison url.

Instruction count

• Primary benchmarks: no relevant changes found
• Secondary benchmarks: 🎉 relevant improvement found

	mean1	max	count2
Regressions 😿 (primary)	N/A	N/A	0
Regressions 😿 (secondary)	N/A	N/A	0
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	-0.2%	-0.2%	1
All 😿🎉 (primary)	N/A	N/A	0

Max RSS (memory usage)

Results

• Primary benchmarks: no relevant changes found
• Secondary benchmarks: 😿 relevant regression found

	mean1	max	count2
Regressions 😿 (primary)	N/A	N/A	0
Regressions 😿 (secondary)	2.7%	2.7%	1
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	N/A	N/A	0
All 😿🎉 (primary)	N/A	N/A	0

Cycles

Results

• Primary benchmarks: 😿 relevant regression found
• Secondary benchmarks: mixed results

	mean1	max	count2
Regressions 😿 (primary)	2.3%	2.3%	1
Regressions 😿 (secondary)	2.9%	3.8%	4
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	-2.3%	-2.6%	4
All 😿🎉 (primary)	2.3%	2.3%	1

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

@rustbot label: -perf-regression

Footnotes

1. the arithmetic mean of the percent change ↩ ↩² ↩³

2. number of relevant changes ↩ ↩² ↩³